Human phospholipase C-α and DNA sequence encoding the same

ABSTRACT

Genes encoding a human PLC-α polypeptide are provided. An expression vector containing these genes and a transformant having the expression vector are provided. The human PLC-α polypeptide can be produced by cultivating the transformant. The human PLC-α polypeptide is useful as an anti-inflammatory agent. Furthermore, a measurement system for conducting clinical evaluation of canceration can be constructed by using the PLC-α polypeptide.

This application is a 371 PCT/JP94/01572 filed Sep. 22, 1994.

TECHNICAL FIELD

The present invention relates to human phospholipase C-α, which is a secretory protein having an oxidation-reduction activity; genes encoding the human phospholipase C-α; an expression vector containing the genes; and a transformant having the expression vector.

BACKGROUND ART

Phospholipase C-α (hereinafter referred to as PLC-α) has conventionally been considered to belong to the superfamily of various isozymes of phospholipase C (hereinafter referred to as PLC).

PLC is an enzyme hydrolyzing (hereinafter referred to as a PLC activity) glycerophospholipid and sphingophospholipid; which is known to be present in the spleen, the tunica mucosa interstini tenuis, and the placenta, etc. of mammals and to play an important role in a living body. For example, phosphatidylinositol-specific phospholipase C (PI-PLC), which is widely present in a living body, hydrolyzes phosphatidylinositol 4,5-diphosphate to generate 1,2-diacylglycerol and inositol 1,4,5-triphosphate (Rhee, S.G. et al., Science 244, pp. 546-550 (1989)). There are a number of reports on various isozymes of PLC, for example, as follows: C. F. Bennett et al., Nature 334, pp. 268-270 (1988); Y. Emori et al., J. Biol. Chem. 264, pp. 21885-21890 (1989); M. Katan et al., Cell 54, pp. 171-177 (1988); S. Ohta et al., FEBS Lett. 242, pp. 31-35 (1988); M. L. Stahl et al., Nature 332, pp. 269-272 (1988); P. G. Suh et al., Cell 54, pp. 161-169 (1988); and R. W. Kritz et al., CIBA Found. Symp. 150, pp. 112-127 (1990).

In terms of function, the above-mentioned PLC-α is not well known; however, the expression thereof is known to increase in a living body being subject to stress and having cancerous tissue.

Regarding the PLC-α of mammals; those of mice (W. M. Hempel et al., J. Immunol. 146, pp. 3713-3720 (1991)), rats (C. F. Bennett et al., Nature 334, pp. 268-270 (1988)), and bovines (Hirano et al., Extended Abstracts, 4L-23, The 15th Annual Meeting of The Japanese Society of Molecular Biology, 1992), have been reported. The PLC-α of these mammals does not have significant homology with any of known sequences of the other known PLC family members.

The PLC-α of the above-mentioned mammals has a conserved amino acid sequence, Trp-Cys-Gly-His-Cys-Lys,[SEQ ID NO:5] at two places. This conserved amino acid sequence is identical with or very similar to the amino acid sequence of an active site for oxidation-reduction activity of protein disulfide isomerase (PDI) and thioredoxin. PDI and thioredoxin are both multifunctional proteins which function as protein disulfide reductase and isomerase, and catalyze the conversion of a thiol group to a disulfide group. PDI of mammals has two conserved sequences in its amino acid sequence, which are homologous to the above-mentioned PLC-α. Thioredoxin of prokaryotes and eukaryotes has one sequence, Trp-Cys-Gly-Pro-Cys-Lys, [SEQ ID NO:6]in its amino acid sequence which is similar to the conserved sequence as shown above. Cys residues in these sequences are respectively assumed to be active sites of catalytic activity (A. Holmgren, J. Biol. Chem. 264, pp. 13963-13966; R. B. Freedman, Cell 57, pp. 1069-1702).

The inventors of the present invention have found that bovine PLC-α expressed in E. coli is a secretory protein which does not functionally have PLC activity and has the activity of reducing a disulfide bond of protein such as insulin (Hirano et al., Cloning of bovine PLC-α and biological significance thereof, Extended Abstracts, 4L-23, The 15th Annual Meeting of The Japanese Society of Molecular Biology, 1992). Thus, PLC-α is not supposed to belong to the PLC superfamily but to the oxidation-reduction control protein family; and its nomenclature has accordingly been changed to thymuredoxin (Hirano et al. supra). This is supported by the above-mentioned consensus of the sequence.

The oxidation-reduction control protein family including PLC-α, thioredoxin, PDI, etc. is considered to be required for maintaining the normal function of a living body. Hereinafter, findings obtained from various reports on various members of the oxidation-reduction control protein family will be shown.

PLC-α has its expression level increased in animal cells transformed with oncogenes, v-src gene; therefore, it is considered to be related to carcinogenesis (H. Hirai et al., Genes Dev 4, pp. 2342-2352 (1990), Mol. Cell. Biol. 10, pp. 1307-1318 (1990), Proc. Natl. Acad. Sci. U.S.A. 87, pp. 8592-8596 (1990)).

Human thioredoxin, also called adult T-cell leukemia (ATL) derived factor, is known to induce the expression of interleukin-2 receptor and stimulate the multiplication of cells (Y. Tagaya et al., EMBO J. 8, pp. 757-764 (1989)).

The protein level of thioredoxin is generally high in actively expanding tissue and the mRNA level of thioredoxin increases (S. W. Jones et al., J. Biol. Chem. 263, pp. 9607-9611 (1988)). As one of functional mechanisms maintaining the normal cell morphology and function of the oxidation-reduction protein control family, controls of the relationships between DNA and protein and between proteins through a Cys residue are considered. This is described in the following document incorporated in the present specification for reference.

The binding of fos and Jun heterodimers to DNA, which relates to v-jun genes and v-fos genes having activity as oncogenes, is regulated by the oxidation-reduction control of a conserved Cys residue in a DNA binding region of these two kinds of proteins: thioredoxin can catalyzes this regulation (C. Abate et al., Science 249, pp. 1157-1161 (1991)). Receptor type tyirosinekinase (1tk) is regulated through the change in a cell oxidation-reduction ability, and kinase activity thereof is increased by the formation of a multimer composed of disulfide bonds (A. R. Bauskin et al., Cell 66, pp. 685-696 (1991)).

Although a control factor of a Cys mediated oxidation-reduction ability in vivo has not been identified, PLC-α, thioredoxin, and PDI have a thiol-dependent catalytic activity because of a sequence Trp-Cys-Gly-His-Cys-Lys[SEQ ID NO:] or Trp Cys-gly-Pro-Cys-Lys [SEQ ID NO:6] therefore, there is a possibility that these are control factors.

DISCLOSURE OF THE INVENTION

As described above, PLC-α of mice, rats, and bovines was reported in detail, whereas no reports were found relating to human beings. Therefore, a human PLC-α protein and a DNA sequence encoding the same have been demanded. The present invention solves the above-mentioned conventional problems and its objective is to provide human PLC-α, human PLC--genes, an expression vector containing the genes, and a transformant having the expression vector.

The inventors of the present invention obtained bovine csk protein (S. Noda et al., Nature 351, pp. 69-72 (1991)) from a bovine thymus, partially purified it, and prepared a rabbit polyclonal antiserum against the purified protein. A bovine thymus cDNA library was screened with the antiserum to find a DNA sequence encoding bovine PLC-α genes. Furthermore, we isolated human PLC-α cDNA from a human placenta cDNA library by hybridization using bovine PLC-α cDNA, thereby achieving the present invention.

The polypeptide of the present invention contains an amino acid sequence from Ser at the 25st position to Leu in the 505th position of SEQ ID NO: 2 of the Sequence Listing.

The DNA sequence of the present invention encodes an amino acid sequence from Ser at the 25st position to Leu in the 505th position of SEQ ID NO: 2 of the Sequence Listing.

The expression vector of the present invention has the above-mentioned DNA sequence.

The transformant of the present invention is obtained by introducing the above-mentioned expression vector into a host.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows amino acid sequences of PLC-α genes of a bovine, a human being, and a mouse.

FIG. 2 shows amino acid sequences of human PLC-α genes and human PDI genes.

FIG. 3 shows amino acid sequences of human PLC-α genes and human thioredoxin genes.

FIG. 4 shows measurements of PLC activities in a crude extract, a cytoplasmic fraction, and a membrane fraction of animal cells transformed with bovine PLC-α genes.

FIG. 5 shows measurements of activities to decompose insulin, of wild-type and mutant bovine PLC-α proteins produced in E. coli transformed with wild-type and mutant bovine PLC-α genes.

BEST MODE FOR CARRYING OUT THE INVENTION

The polypeptide and the DNA sequence encoding the same according to the present invention can be prepared, for example, in accordance with the following steps.

(1) Preparation of Human Placenta cDNA Library

A human placenta cDNA library can be prepared by a conventional method. First, total RNA is isolated from a human placenta by, for example, a guani-dine-phenol/chloroform method (Gene, 28 (1984), pp. 263-270), and the isolate is repeatedly subjected to oligo dT cellulose column chromatography to obtain polyA RNA. Double-stranded cDNA is synthesized from the RNA thus obtained. The synthesis of the double-stranded cDNA can be conducted by, for example, a method of Gubler and Hoffman (Gene, 25 (1983), pp. 263-269). An appropriate linker sequence is attached to the double-stranded cDNA thus obtained to form a restriction enzyme cleavage site. Then, the resultant cDNA is inserted into a restriction enzyme Cleavage site of a cloning vector, which is the same as that of the linker sequence, whereby a human placenta cDNA library is prepared. As a cloning vector, a phage vector such as λgt11 is preferably used; however, the cloning vector is not limited thereto and any of the cloning vectors known to those skilled in the art can be used.

(2) Preparation of bovine PLC-α cDNA

(i) Partial Purification of Bovine csk Protein

Bovine csk protein can be partially purified from a bovine thymus by a purification method known to those skilled in the art, e.g., the method of Noda et al.

(ii) Preparation of Polyclonal Antiserum

Polyclonal antiserum can be prepared by a method known to those skilled in the art by, for example, immunizing a rabbit with partially purified bovine csk protein, collecting serum from the rabbit, and partially purifying the serum by ammonium sulfate fractionation. Synthesized bovine csk protein or a fragment thereof can be used in place of the partially purified bovine csk protein.

(iii) Preparation of Bovine Thymus cDNA Library

A bovine thymus cDNA library can be prepared, using a bovine thymus as a material by a conventional method, as in the above-mentioned (1) Preparation of human placenta cDNA library.

(iv) Isolation of Bovine Thymus cDNA Phage Clones

The analysis of the bovine thymus cDNA library obtained in the above (iii) can be conducted by screening plaques derived from phage in which the bovine thymus cDNA has been inserted, with the polyclonal antiserum obtained in the above (ii), using, for example, ProtoBlot system (produced by Promega). Thus, positive phage clones containing the bovine PLC-α protein DNA fragment can be isolated.

(v) Sequencing of Bovine Thymus cDNA

Sequencing of the DNA insert of the positive phage clones obtained in the above (iv) can be conducted directly by a method known to those skilled in the art, for example, using a DNA sequencing kit. Alternatively, sequencing can be conducted by using phage DNA containing the DNA insert prepared from the clones. The preparation of the phage DNA containing the DNA insert can be conducted by, for example, a protocol of Maniatis et al., Molecular Cloning, A Laboratory manual, Cold Spring Harbor Laboratory Press, New York (1982). The DNA sequence of the bovine thymus cDNA clones thus sequenced and the amino acid sequence corresponding thereto are shown in SEQ ID NO: 3 of the Sequence Listing.

(3) Isolation of Human Thymus cDNA Phage Clones

Positive phage clones containing a human PLC-α DNA fragment can be isolated by screening the human placenta cDNA library obtained in the above (1) using bovine PLC-α cDNA labelled with ³² P as a probe under moderate hybridization conditions. The bovine PLC-α cDNA probe labelled with ³² p can be prepared based on the sequence determined in the above (v) by a method known to those skilled in the art.

(4) Sequencing of Human Thymus cDNA Phage Clones

Sequencing of the DNA insert of the positive phage clones obtained in the above (3) can be conducted by the same method as that of the above (v). The DNA sequence of the human thymus cDNA clones thus determined and the amino, acid sequence corresponding thereto are shown in SEQ ID NO: 1 of the Sequence Listing.

(5) Production of Human PLC-α Protein

Human PLC-α protein can be produced by a genetic recombination technique using a host/expression vector known to those skilled in the art. A number of kinds of combinations between a host and an expression vector can be used for expressing the human PLC-α protein of the present invention. For example, effective expression vectors can contain segments of chromosomes, non-chromosomes, and a synthetic DNA sequence. Various known derivatives of SV40 and known bacterial plasmids are preferable as the vector. Specific examples of the vector include E. coli plasmids such as pCR1, pBR322, pMB9, pET-3A, and derivatives thereof; broad-range host plasmid RP4; a number of derivatives of λ-phage; phage DNA such as M13 and filamentous single-stranded phage DNA; yeast plasmids such as 2 μplasmid or derivatives thereof; and plasmids containing an adenovirus major late promoter enhanced in the presence of SV40 enhancer.

Furthermore, a number of kinds of expression regulatory sequences, i.e., sequences regulating the expression of a DNA sequence when being operably bound by the DNA sequence, can be used in the above-mentioned vector for expressing the human PLC-α protein of the present invention. Examples of such useful expression regulatory sequences include early and late promoters of SV40; early promoters of adenovirus or cytomegalovirus; the lac system; the trp system; the TAC or TRC system; the T7 promoter which is expressed by T7 RNA polymerase; a major operator region and a promoter region of λ-phage; a regulatory region of fd-coated protein; promoters of 3-phosphoglyceratekinase or other glycolytic pathway enzymes; acid phosphatase such as Pho5 promoter, a promoter of yeast α-factor, and polyhedron promoter of Baculovirus; other known sequences regulating the expression of genes of prokaryotic cells, eukaryotic cells, or viruses thereof; and various combinations thereof.

A number of kinds of single-cell host cells are useful for the expression of the human PLC-α protein of the present invention. Examples of the hosts can include E. coli; Pseudomonas; Bacillus; Streptomyces; Saccharomyces and other strains of fungi; Chinese hamster ovary ("CHO") cells and cultivated mouse cells; animal cells such as COS1, COS7, BSC1, BSC40, and BMT1O of the African green monkey; known eukaryotic cells such as cultivated insect cells, cultivated human cells, cultivated plant cells; and procaryotic cells.

A vector having a DNA sequence of the above human PLC-α polypeptide is introduced into a host to obtain a transformant. A human PLC-α polypeptide can be produced by cultivating the transformant in an appropriate culture medium.

According to the present invention, as described above, human PLC-α which is a secretory protein having oxidation-reduction activity, human PLC-α genes, an expression vector containing the genes, and a transformant halving the expression vector are provided.

The polypeptide of the present invention has a conserved sequence which is identical with or very similar to an active site of thioredoxin stimulating the multiplication of cells and has an activity of reducing a disulfide bond of protein, and can therefore be utilized as an anti-inflammatory agent. Furthermore, the expression of PLC-α increases in a living body which is cancerated or is subject to stress, so that PLC-α functions as an indicator of these conditions and can provide a measurement system of clinical evaluation of these conditions.

EXAMPLES

Hereinafter, the present invention will be described by way of illustrative examples.

Example 1

(1) Preparation of Human Placenta cDNA Library

The first strand and the second strand of cDNA were synthesized from polyA RNA prepared from a human placenta. EcoRI-NotI-BamHI adaptors were attached to both ends of the double-stranded DNA thus obtained. The resultant DNA was inserted into vector λZAPII to prepare a human placenta cDNA library.

(2) Preparation of Bovine PLC-α cDNA

(i) Partial Purification of Bovine csk Protein

A peptide having an amino acid sequence Gly-Thr-Phe-Leu-Val-Arg-Glu-Ser which is a part of csk protein and is conserved in an SH2 (Src.Homology2) portion common to the src protein family was synthesized. Antiserum against this peptide was prepared from a rabbit. Then csk, which is 50 kD protein partially purified from a bovine thymus, was obtained by Western blotting method using this antiserum.

(ii) Preparation of Polyclonal Antiserum

A rabbit was immunized with partially purified bovine csk protein, and serum was collected from the rabbit. The serum was partially purified by ammonium sulfate fractionation to obtain antiserum. The antiserum thus obtained was named polyclonal antiserum 507.

(iii) Preparation of Bovine Thymus cDNA Library

The first strand and the second strand of cDNA were synthesized from polyA RNA prepared from a bovine thymus. EcoRI linkers were attached to both ends of the double-stranded DNA thus obtained. The resultant DNA was inserted into an EcoRI site of vector λgtll to obtain a cDNA library.

(iv) Isolation and Sequencing of Bovine Thymus cDNA clones

The analysis of the bovine thymus cDNA library obtained in the above (iii) was conducted by screening 1.8×10⁶ plaques derived from phage λgtll in which the bovine thymus cDNA was inserted, with polyclonal antiserum507 using the ProtoBlot system (produced by Promega), whereby 3 positive phage clones were isolated. More specifically, the above cDNA library was plated with E. coli Y109OR⁻ and was cultivated at 43° C. for 4 hours until small plaques were generated. Thereafter, a nitrocellulose sheet (Hybond C-Extra, produced by Amersham) previously soaked in IPTG inducing the expression from lac promoter of vector λllgt was placed on the plate containing these small plaques. The plate was kept warm for 3 hours. Then, the nitrocellulose sheet was carefully peeled off and positive phage clones reactive to polyclonal antiserum 507 were identified.

Both strands of phage clone λ12 having the largest insert of 1.8 kb of the phage clones obtained in the above (iv) were sequenced with Sequenase 2.0 (produced by USB) by generating nested deletions at each strand with Exonuclease III (produced by Pharmacia).

The homology between the determined sequence and the known sequence was examined by using a DDBJ (DNA Data Bank of Japan) database in accordance with FASTA and TFASTA programs (W. R. Peason et al., Proc. Natn. Acad. Sci. U.S.A. 85, pp. 2444-2448 (1988)). As a result, the determined sequence was found to be a DNA sequence similar to that of bovine PLC-α but lacking a 5'-portion. The same library was screened using an EcoRI-EcoRV fragment (positioned closest to the 5'-terminus of a phage clone λ12 insert) of the phage clone λ12 insert, whereby phage clone λ21 having a DNA insert longer than, a phage clone λ12 insert was obtained. The sequence of the insert of the phage clone λ21l thus obtained was determined in the same manner as the above and indicated that the phage clone λ21 contained full length sequence of a bovine PLC-α having the 5'-portion sequence. The full length DNA sequence of bovine PLC-α thus obtained and the amino acid sequence corresponding thereto are shown in SEQ ID NO: 3 of the Sequence Listing.

(3) Isolation of Human Placenta cDNA Phage Clones

In order to obtain a human PLC-α cDNA phage alone, the λZAPII human placenta cDNA library obtained in the above (1) was screened using the DNA insert of the phage clone λ21 labelled with ³² p as a probe under the moderate hybridization conditions to obtain positive phage clones named λ17. The sequence of the insert in the phage clone thus obtained was determined by the same method as that of the above (1)(v). The full length DNA, sequence of human PLC-α thus obtained and the amino acid sequence corresponding thereto are shown in SEQ ID NO: 1 of the Sequence Listing.

The determined amino acid sequences of bovine and human PLC-α and the amino acid sequence of the known mouse PLC-α (Hempel et al, supra) are shown in FIG. 1. The bovine and human PLC-α cDNA sequences thus obtained were composed of 1515 bp of open reading frame and encoded a polypeptide including 505 amino acids having a hydrophobic N-terminal signal peptide (amino acid residues 24 to 1). The molecular weight of the respective polypeptides were calculated to be 56,895 Da and 56,698 Da. The amino acid sequence of bovine PLC-α had 90%, 87%, and 94% homology with mouse, rat, and human PLC-α sequences, respectively.

FIG. 2 shows the determined human PLC-α and the known human protein disulfide reductase (hereinafter, referred to as PDI) (T. Pihlajaniemi et al., EMBO J. 6, pp. 643-649 (1987)). The human PLC-α had 56% homology and 32% similarity with human PDI at an amino acid level.

FIG. 3 shows the determined human PLC-α sequence and the known human thioredoxin sequence. The amino acids from the 1st to 105th positions of the human PLC-α sequence showed 55% homology and 23% similarity with human thioredoxin (Y. Tagaya et al., EMBO J. 8, pp. 757-764 (1989)).

Example 2

Sense vector PLC-α (expression vector) in which the bovine PLC-α cDNA sequence obtained in Example 1 was inserted downstream of a β-actin promoter of the mammal cell expression vector pUC-CAGGS in the forward direction and an antisense vector in which the bovine PLC-α cDNA sequence was inserted in the reverse direction were constructed. NIH3T3 mouse fibroblast was transformed together with pSV2NEO, using the sense vector and the antisense vector by a calcium phosphate coprecipitation method known to those skilled in the art. The transformant thus obtained was selected with 800 μg/ml of G418, whereby three kinds of independent stable transformants (named F01, F02, and F03) in which a sense vector is introduced and which expresses bovine PLC-α protein at a high level and two kinds of independent transformants (named R01 and R06) in which the antisense vector is introduced were obtained.

The cells of the transformants F01, F02, F03, R01, and R06 thus obtained were collected and dissolved in an ice-cooled cell lysing solution containing 50 mM of Tris-HCl (pH 7.4), 150 mM of NaCl, 0.05% (W/V) sodium dodecyl sulfate, 1% (v/v) triton X-100, 10 U/ml of aprotinin, 2 mM of PMSF, 100 mg/l of leupeptin, and 1 mM of ortho-vanadyl sodium. The solution thus obtained was subjected to SDS-PAGE using 9% acrylamide and transferred to a polyvinylidene difluoride film (produced by Millipore). The PLC-α expression level of three kinds of cell lines was measured by immunoblotting using polyclonal antiserum 507. The PLC-α expression level of three kinds of stable transformants is 10 to 15 times as high as endogenous PLC-α.

A crude extract, a cytoplasmic fraction, and a membrane fraction of these five cell lines were prepared in accordance with a method of Kato et al. (J. Biol. Chem. 267, pp. 6483-6487 (1991)). The PLC activity in the crude extract, the cytoplasmic fraction, and the membrane fraction thus obtained was measured by the method of Kato et al. using [³ H]PtdIns 4,5-P₂ as a substrate. FIG. 4 shows the measurement result. In this figure, a presents the PLC activity of the crude extract, b presents that of in the cytoplasmic fraction, and c presents that of the membrane fraction. As shown in this figure, in any of the fractions, the PLC activities were not substantially different among the respective cell lines.

Example 3

Mammal PLC-α has an amino acid sequence which is completely the same sequence as that of an oxidation-reduction active site of PDI in its amino acid sequence; therefore, the PLC-α was assumed to have the reduction function similar to that of PDI. The reduction function of wild-type and mutant bovine PLC-α proteins expressed in E. coli was measured by a known assay (A. Holmgren, J. Biol. Chem. 254, pp. 9627-9632 (1979)) for measuring the decomposition of insulin in dithiothreitol.

(1) Expression of Bovine PLC-α Protein

First, 1.8 kb of insert of phage clone λ12 obtained in Example 1 was treated with Mung bean nuclease so as to obtain blunt ends. The fragment thus obtained was sub-cloned at a SmaI site of bacterial expression vector pGEX2T (produced by Pharmacia) to construct plasmid pGEX-PLC-α. E. coli XL-1B was transformed with this plasmid. The transformant thus obtained was cultivated overnight by a conventional method, and the culture broth thus obtained was diluted with a fresh medium at a dilution rate of 1:10, followed by being cultivated at 25° C. Eighteen hours later, 0.1 ml of IPTG was added to the culture broth and the resultant culture solution was cultivated for another 6 hours; whereby, the expression of 1.8 kb insert was induced. The E. coli cells were lysed in a lysing buffer containing 50 mM of Tris-HCl (pH 7.5), 25% sucrose, 0.5 NP-40, and 5 mM of MgC'₂ by freeze-thawing. The lysate was purified by centrifugation to obtain supernatant. The supernatant was filtrated with 1.2 μm Acrodisc (produced by GelmanSciences), and the filtrate thus obtained was subjected to glutathione Sepharose 4B (produced by Pharmacia) column. The column was washed with a buffer containing 20 mM of Tris-HCl (pH 7.5), 2 mM of MgCl₂, and 1 mM of dithiothreitol. The filtrate was eluted with an elution buffer containing 5 mM glutathione and 50 mM of Tris-HCl (pH 9.5). The eluate was fractionated by 1.5 ml portions, followed by being analyzed by electrophoresis using an 8% SDS-polyacrylamide gel. Fractions containing PLC-α protein were collected and dialyzed against a dialysis buffer containing 20 mM of Tris-HCl (pH 7.5) and 10 mM of dithiothreitol. The dialyzed sample was incubated with a digestive buffer containing 2.5 mM of CaCl₂, 50 mM of Tris-HCl (pH 7.5), 150 mM of NaCl, and 400 U of human thrombin per milligram of protein at room temperature for 1.5 hours. This sample liquid was subjected to Sephadex 16/60 (produced by Pharmacia) equilibrated with a phosphate buffer and was eluted at 1 ml/min. The fractions thus obtained were analyzed with 12% SDS-PAGE and fractions containing bovine PLC-α protein were collected. The fractions thus collected were dialyzed against water and lyophilized to obtain PLC-α protein. This protein is wild-type PLC-α.

Then, a conserved sequence, Trp-Cys-Gly-His-Cys-Lys, was subjected to specific site-directed mutation in order to prepare a mutant PLC-α DNA sequence. The site-directed mutagenesis was conducted by using the Muta-Gene Kit (produced by Bio-Rad). Mutagenic primers, 5'GCCCCCTGGT CTCCACACAG CAAAAAGCTT [SEQ ID NO:7] (sense) and GCTCCTTGGT CTGGTCACTC TAAGAATCTG [SEQ ID NO:8] (sense), change Cys at the 57th and 60th positions into Ser, and Cys at the 406th and 409th positions into Ser, respectively. The site-directed mutagenesis thus obtained was confirmed by determining the base sequence. In the mutant PLC-α protein, in both of the two conserved sequences 4 Cys residues in total were replaced by Ser. More specifically, the mutant PLC-α protein has two Trp-Ser-Gly-His-Ser-Lys [SEQ ID NO:5] sequences. The mutant PLC-α DNA sequence was expressed in E. coli in the same way as in the wild-type PLC-α DNA sequence to obtain a mutant PLC-α protein.

(2) Standard Assay for Measuring Decomposition of Insulin

Assay for measuring the decomposition of insulin was conducted in the same way as in Holgeman et al. (supra) except that the reaction volume was 60 μl. Nonenzymatic decomposition of insulin with dithiothreitol was recorded as a control. E. coli thioredoxin was purchased from Promega.

The measurement result of the standard assay is shown in FIG. 5. In this figure, as represented by curves of closed circles and open squares with a dot, wild-type bovine PLC-α had an activity for reducing insulin; as represented by a curve of open squares, mutant bovine PLC-α did not have an activity for reducing insulin. In this assay, thioredoxin represented by curves of open squares and closed squares had an activity 2 to 3 times that of bovine PLC-α per mole of protein.

As is apparent from these results, it was found that PLC-α has an ability of catalyzing the reduction of disulfide bonds in the same way as in thioredoxin, and two Cys residues in the sequence Trp-Cys-Gly-His-Cys-Lys [SEQ ID NO:5] are indispensable for oxidation-reduction activity.

Example 4

Secretory PLC-α produced by the transformants F02 and R06 obtained in Example 2 was detected. F02 and R06 transformant cells were grown in 150 mm culture plates each containing DMEM culture medium (produced by GIBCO) with 10% bovine serum added. The grown cells were washed with a phosphate buffer and cultivated in 20 ml serum-free culture medium (Cell Grosser P. Sumitomo Pharmaceuticals Co.). Ten hours later, culture medium was collected and centrifuged at 4° C., 100,000 g for 1 hour, and then supernatant was recovered. The supernatant was dialyzed against water, followed by being lyophilized. Thereafter, immunoblotting was conducted using polyclonal antiserum 507 in the same way as in Example 2, whereby secretory PLC-α was detected. Immunoblotting indicated that an excess amount of secretory PLC-α was produced in the supernatant of the F02 cell, and a small amount of secretory PLC-α was even produced in the R06 cell.

Furthermore, the F02 and R06 transformant cells grown in the culture plates by the same method as the above were washed in DMEM culture medium containing no methionine. Those cells were labelled in vivo with [³⁵ S]Met of 1 mCi at 37° C. in DMEM culture medium which contained 15 ml of 1% dialyzed bovine serum and did not contain methionine. The culture supernatant of the transformant cell labelled in vivo was obtained by cultivating with the same method as that of Example 4. The culture supernatant thus obtained was subjected to 9% SDS-PAGE and exposed to Fuji Bass Imaging Plate c (produced by Fuji) to detect secretory PLC-α. As a result, it was confirmed that PLC-α was secreted at a high level in the culture supernatant.

    __________________________________________________________________________     #             SEQUENCE LISTING                                                   - -  - - (1) GENERAL INFORMATION:                                              - -    (iii) NUMBER OF SEQUENCES: 8                                            - -  - - (2) INFORMATION FOR SEQ ID NO:1:                                      - -      (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 1933 base - #pairs                                                 (B) TYPE: nucleic acid                                                         (C) STRANDEDNESS: double                                                       (D) TOPOLOGY: linear                                                  - -     (ii) MOLECULE TYPE: cDNA to mRNA                                       - -     (ix) FEATURE:                                                                   (A) NAME/KEY: CDS                                                              (B) LOCATION: 68..1585                                                - -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:1:                                - - GGCGCCGACC TCCGCAGTCC CAGCCGAGCC GCGACCCTTC CGGCCGTCCC CA -              #CCCCACCT     60                                                                  - - CGCCGCC ATG CGC CTC CGC CGC CTA GCG CTG TTC - #CCG GGT GTG GCG CTG           109                                                                                Met Arg Leu Arg Arg Leu - #Ala Leu Phe Pro Gly Val Ala Leu                       1        - #       5           - #       10                           - - CTT CTT GCC GCG GCC CGC CTC GCC GCT GCC TC - #C GAC GTG CTA GAA CTC           157                                                                        Leu Leu Ala Ala Ala Arg Leu Ala Ala Ala Se - #r Asp Val Leu Glu Leu             15                 - # 20                 - # 25                 - # 30        - - ACG GAC GAC AAC TTC GAG AGT CGC ATC TCC GA - #C ACG GGC TCT GCG GGC           205                                                                        Thr Asp Asp Asn Phe Glu Ser Arg Ile Ser As - #p Thr Gly Ser Ala Gly                             35 - #                 40 - #                 45               - - CTC ATG CTC GTC GAG TTC TTC GCT CCC TGG TG - #T GGA CAC TGC AAG AGA           253                                                                        Leu Met Leu Val Glu Phe Phe Ala Pro Trp Cy - #s Gly His Cys Lys Arg                         50     - #             55     - #             60                   - - CTT GCA CCT GAG TAT GAA GCT GCA GCT ACC AG - #A TTA AAA GGA ATA GTC           301                                                                        Leu Ala Pro Glu Tyr Glu Ala Ala Ala Thr Ar - #g Leu Lys Gly Ile Val                     65         - #         70         - #         75                       - - CCA TTA GCA AAG GTT GAT TGC ACT GCC AAC AC - #T AAC ACC TGT AAT AAA           349                                                                        Pro Leu Ala Lys Val Asp Cys Thr Ala Asn Th - #r Asn Thr Cys Asn Lys                 80             - #     85             - #     90                           - - TAT GGA GTC AGT GGA TAT CCA ACC CTG AAG AT - #A TTT AGA GAT GGT GAA           397                                                                        Tyr Gly Val Ser Gly Tyr Pro Thr Leu Lys Il - #e Phe Arg Asp Gly Glu             95                 - #100                 - #105                 - #110        - - GAA GCA GGT GCT TAT GAT GGA CCT AGG ACT GC - #T GAT GGA ATT GTC AGC           445                                                                        Glu Ala Gly Ala Tyr Asp Gly Pro Arg Thr Al - #a Asp Gly Ile Val Ser                            115  - #               120  - #               125               - - CAC TTG AAG AAG CAG GCA GGA CCA GCT TCA GT - #G CCT CTC AGG ACT GAG           493                                                                        His Leu Lys Lys Gln Ala Gly Pro Ala Ser Va - #l Pro Leu Arg Thr Glu                        130      - #           135      - #           140                   - - GAA GAA TTT AAG AAA TTC ATT AGT GAT AAA GA - #T GCC TCT ATA GTA GGT           541                                                                        Glu Glu Phe Lys Lys Phe Ile Ser Asp Lys As - #p Ala Ser Ile Val Gly                    145          - #       150          - #       155                       - - TTT TTC GAT GAT TCA TTC AGT GAG GCT CAC TC - #C GAG TTC CTA AAA GCA           589                                                                        Phe Phe Asp Asp Ser Phe Ser Glu Ala His Se - #r Glu Phe Leu Lys Ala                160              - #   165              - #   170                           - - GCC AGC AAC TTG AGG GAT AAC TAC CGA TTT GC - #A CAT ACG AAT GTT GAG           637                                                                        Ala Ser Asn Leu Arg Asp Asn Tyr Arg Phe Al - #a His Thr Asn Val Glu            175                 1 - #80                 1 - #85                 1 -       #90                                                                               - - TCT CTG GTG AAC GAG TAT GAT GAT AAT GGA GA - #G GGT ATC ATC TTA         TTT      685                                                                     Ser Leu Val Asn Glu Tyr Asp Asp Asn Gly Gl - #u Gly Ile Ile Leu Phe                           195  - #               200  - #               205               - - CGT CCT TCA CAT CTC ACT AAC AAG TTT GAG TA - #C AAG ACT GTG GCA TAT           733                                                                        Arg Pro Ser His Leu Thr Asn Lys Phe Glu Ty - #r Lys Thr Val Ala Tyr                        210      - #           215      - #           220                   - - ACA GAG CAA AAA ATG ACC AGT GGC AAA ATT AA - #A AAG TTT ATC CAG GAA           781                                                                        Thr Glu Gln Lys Met Thr Ser Gly Lys Ile Ly - #s Lys Phe Ile Gln Glu                    225          - #       230          - #       235                       - - AAC ATT TTT GGT ATC TGC CCT CAC ATG ACA GA - #G GAC AAT AAA GAT TTG           829                                                                        Asn Ile Phe Gly Ile Cys Pro His Met Thr Gl - #u Asp Asn Lys Asp Leu                240              - #   245              - #   250                           - - ATA CAG GGC AAG GAC TTA CTT ATT GCT TAC TA - #T GAT GTG GAC TAT GAA           877                                                                        Ile Gln Gly Lys Asp Leu Leu Ile Ala Tyr Ty - #r Asp Val Asp Tyr Glu            255                 2 - #60                 2 - #65                 2 -       #70                                                                               - - AAG GAC GCT AAA GGT TCC AAC TAC TGG AGA AA - #C AGG GTA ATG ATG         GTG      925                                                                     Lys Asp Ala Lys Gly Ser Asn Tyr Trp Arg As - #n Arg Val Met Met Val                           275  - #               280  - #               285               - - GCA AAG AAA TTC CTG GAT GCT GGG CAC AAA CT - #C AAC TTT GCT GTA GCT           973                                                                        Ala Lys Lys Phe Leu Asp Ala Gly His Lys Le - #u Asn Phe Ala Val Ala                        290      - #           295      - #           300                   - - AGC CGC AAA ACC TTT AGC CAT GAA CTT TCT GA - #T TTT GGC TTG GAG AGC          1021                                                                        Ser Arg Lys Thr Phe Ser His Glu Leu Ser As - #p Phe Gly Leu Glu Ser                    305          - #       310          - #       315                       - - ACT GCT GGA GAG ATT CCT GTT GTT GCT ATC AG - #G ACT GCT AAA GGA GAG          1069                                                                        Thr Ala Gly Glu Ile Pro Val Val Ala Ile Ar - #g Thr Ala Lys Gly Glu                320              - #   325              - #   330                           - - AAG TTT GTC ATG CAG GAG GAG TTC TCG CGT GA - #T GGG AAG GCT CTG GAG          1117                                                                        Lys Phe Val Met Gln Glu Glu Phe Ser Arg As - #p Gly Lys Ala Leu Glu            335                 3 - #40                 3 - #45                 3 -       #50                                                                               - - AGG TTC CTG CAG GGT TAC TTT GGT GGC AAT CT - #G AAG AGA TAC CTG         AAG     1165                                                                     Arg Phe Leu Gln Gly Tyr Phe Gly Gly Asn Le - #u Lys Arg Tyr Leu Lys                           355  - #               360  - #               365               - - TCT GAC CCT ATC CCA GAG AGC AAT GAT GGG CC - #T GTG AAG GTA GTG GTA          1213                                                                        Ser Asp Pro Ile Pro Glu Ser Asn Asp Gly Pr - #o Val Lys Val Val Val                        370      - #           375      - #           380                   - - GCA GAG AAT TTT GAT GAA ATA GTG AAT AAT GA - #A AAT AAA GAT GTG CTG          1261                                                                        Ala Glu Asn Phe Asp Glu Ile Val Asn Asn Gl - #u Asn Lys Asp Val Leu                    385          - #       390          - #       395                       - - ATT GAA TTT TAT GCC CCT TGG TGT GGT CAT TG - #T AAG AAC CTG GAG CCC          1309                                                                        Ile Glu Phe Tyr Ala Pro Trp Cys Gly His Cy - #s Lys Asn Leu Glu Pro                400              - #   405              - #   410                           - - AAG TAT AAA GAA CTT GGC GAG AAG CTC AGC AA - #A GAC CCA AAT ATC GTC          1357                                                                        Lys Tyr Lys Glu Leu Gly Glu Lys Leu Ser Ly - #s Asp Pro Asn Ile Val            415                 4 - #20                 4 - #25                 4 -       #30                                                                               - - ATA GCC AAG ATG GAT GCC ACA GCC AAT GAT GT - #G CCT TCT CCA TAT         GAA     1405                                                                     Ile Ala Lys Met Asp Ala Thr Ala Asn Asp Va - #l Pro Ser Pro Tyr Glu                           435  - #               440  - #               445               - - GTC AGA GGT TTT CCT ACC ATA TAC TTC TCT CC - #A GCC AAC AAG AAG CTA          1453                                                                        Val Arg Gly Phe Pro Thr Ile Tyr Phe Ser Pr - #o Ala Asn Lys Lys Leu                        450      - #           455      - #           460                   - - AAT CCA AAG AAA TAT GAA GGT GGC CGT GAA TT - #A AGT GAT TTT ATT AGC          1501                                                                        Asn Pro Lys Lys Tyr Glu Gly Gly Arg Glu Le - #u Ser Asp Phe Ile Ser                    465          - #       470          - #       475                       - - TAT CTA CAA AGA GAA GCT ACA AAC CCC CCT GT - #A ATT CAA GAA GAA AAA          1549                                                                        Tyr Leu Gln Arg Glu Ala Thr Asn Pro Pro Va - #l Ile Gln Glu Glu Lys                480              - #   485              - #   490                           - - CCC AAG AAG AAG AAG AAG GCA CAG GAG GAT CT - #C TAA AGCAGTAGCC               1595                                                                        Pro Lys Lys Lys Lys Lys Ala Gln Glu Asp Le - #u  *                             495                 5 - #00                 5 - #05                             - - AAACACCACT TTGTAAAAGG ACTCTTCCAT CAGAGATGGA AAACCATTGG GG -              #AGGGACTA   1655                                                                  - - GGACCCATAT GGGAATTATT ACCTCTCAGG GCCGAGAGGA CAGAATGGAA AT -             #AATCTGAA   1715                                                                  - - TCCTGTTAAA TTTTCTCTAA ACTGTTTCTT AGCTGCACTG TTTATGGAAA TA -             #CCAGGAAC   1775                                                                  - - CAGTTTATGT TTGTGGTTTT GGGAAAAATT ATTTGTGTTG GGGGAAATGT TG -             #TGGGGGTG   1835                                                                  - - GGGTTGAGTT GGGGGATATT TTCTAATTTT TTTTGTACAT TTGGAACAGT GA -             #CCAATAAA   1895                                                                  - - TGAGACCCCT TTAAACTGTC AAAAAAAAAA AAAAAAAA      - #                       - #   1933                                                                      - -  - - (2) INFORMATION FOR SEQ ID NO:2:                                      - -      (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH:  506 ami - #no acids                                               (B) TYPE: amino acid                                                           (D) TOPOLOGY: linear                                                  - -     (ii) MOLECULE TYPE: protein                                            - -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:2:                                - - Met Arg Leu Arg Arg Leu Ala Leu Phe Pro Gl - #y Val Ala Leu Leu Leu         1               5 - #                 10 - #                 15               - - Ala Ala Ala Arg Leu Ala Ala Ala Ser Asp Va - #l Leu Glu Leu Thr Asp                    20     - #             25     - #             30                   - - Asp Asn Phe Glu Ser Arg Ile Ser Asp Thr Gl - #y Ser Ala Gly Leu Met                35         - #         40         - #         45                       - - Leu Val Glu Phe Phe Ala Pro Trp Cys Gly Hi - #s Cys Lys Arg Leu Ala            50             - #     55             - #     60                           - - Pro Glu Tyr Glu Ala Ala Ala Thr Arg Leu Ly - #s Gly Ile Val Pro Leu        65                 - # 70                 - # 75                 - # 80        - - Ala Lys Val Asp Cys Thr Ala Asn Thr Asn Th - #r Cys Asn Lys Tyr Gly                        85 - #                 90 - #                 95               - - Val Ser Gly Tyr Pro Thr Leu Lys Ile Phe Ar - #g Asp Gly Glu Glu Ala                   100      - #           105      - #           110                   - - Gly Ala Tyr Asp Gly Pro Arg Thr Ala Asp Gl - #y Ile Val Ser His Leu               115          - #       120          - #       125                       - - Lys Lys Gln Ala Gly Pro Ala Ser Val Pro Le - #u Arg Thr Glu Glu Glu           130              - #   135              - #   140                           - - Phe Lys Lys Phe Ile Ser Asp Lys Asp Ala Se - #r Ile Val Gly Phe Phe       145                 1 - #50                 1 - #55                 1 -       #60                                                                               - - Asp Asp Ser Phe Ser Glu Ala His Ser Glu Ph - #e Leu Lys Ala Ala         Ser                                                                                              165  - #               170  - #               175              - - Asn Leu Arg Asp Asn Tyr Arg Phe Ala His Th - #r Asn Val Glu Ser Leu                   180      - #           185      - #           190                   - - Val Asn Glu Tyr Asp Asp Asn Gly Glu Gly Il - #e Ile Leu Phe Arg Pro               195          - #       200          - #       205                       - - Ser His Leu Thr Asn Lys Phe Glu Tyr Lys Th - #r Val Ala Tyr Thr Glu           210              - #   215              - #   220                           - - Gln Lys Met Thr Ser Gly Lys Ile Lys Lys Ph - #e Ile Gln Glu Asn Ile       225                 2 - #30                 2 - #35                 2 -       #40                                                                               - - Phe Gly Ile Cys Pro His Met Thr Glu Asp As - #n Lys Asp Leu Ile         Gln                                                                                              245  - #               250  - #               255              - - Gly Lys Asp Leu Leu Ile Ala Tyr Tyr Asp Va - #l Asp Tyr Glu Lys Asp                   260      - #           265      - #           270                   - - Ala Lys Gly Ser Asn Tyr Trp Arg Asn Arg Va - #l Met Met Val Ala Lys               275          - #       280          - #       285                       - - Lys Phe Leu Asp Ala Gly His Lys Leu Asn Ph - #e Ala Val Ala Ser Arg           290              - #   295              - #   300                           - - Lys Thr Phe Ser His Glu Leu Ser Asp Phe Gl - #y Leu Glu Ser Thr Ala       305                 3 - #10                 3 - #15                 3 -       #20                                                                               - - Gly Glu Ile Pro Val Val Ala Ile Arg Thr Al - #a Lys Gly Glu Lys         Phe                                                                                              325  - #               330  - #               335              - - Val Met Gln Glu Glu Phe Ser Arg Asp Gly Ly - #s Ala Leu Glu Arg Phe                   340      - #           345      - #           350                   - - Leu Gln Gly Tyr Phe Gly Gly Asn Leu Lys Ar - #g Tyr Leu Lys Ser Asp               355          - #       360          - #       365                       - - Pro Ile Pro Glu Ser Asn Asp Gly Pro Val Ly - #s Val Val Val Ala Glu           370              - #   375              - #   380                           - - Asn Phe Asp Glu Ile Val Asn Asn Glu Asn Ly - #s Asp Val Leu Ile Glu       385                 3 - #90                 3 - #95                 4 -       #00                                                                               - - Phe Tyr Ala Pro Trp Cys Gly His Cys Lys As - #n Leu Glu Pro Lys         Tyr                                                                                              405  - #               410  - #               415              - - Lys Glu Leu Gly Glu Lys Leu Ser Lys Asp Pr - #o Asn Ile Val Ile Ala                   420      - #           425      - #           430                   - - Lys Met Asp Ala Thr Ala Asn Asp Val Pro Se - #r Pro Tyr Glu Val Arg               435          - #       440          - #       445                       - - Gly Phe Pro Thr Ile Tyr Phe Ser Pro Ala As - #n Lys Lys Leu Asn Pro           450              - #   455              - #   460                           - - Lys Lys Tyr Glu Gly Gly Arg Glu Leu Ser As - #p Phe Ile Ser Tyr Leu       465                 4 - #70                 4 - #75                 4 -       #80                                                                               - - Gln Arg Glu Ala Thr Asn Pro Pro Val Ile Gl - #n Glu Glu Lys Pro         Lys                                                                                              485  - #               490  - #               495              - - Lys Lys Lys Lys Ala Gln Glu Asp Leu  *                                                500      - #           505                                          - -  - - (2) INFORMATION FOR SEQ ID NO:3:                                      - -      (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 1942 base - #pairs                                                 (B) TYPE: nucleic acid                                                         (C) STRANDEDNESS: double                                                       (D) TOPOLOGY: linear                                                  - -     (ii) MOLECULE TYPE: cDNA to mRNA                                       - -     (ix) FEATURE:                                                                   (A) NAME/KEY: CDS                                                              (B) LOCATION: 84..1601                                                - -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:3:                                - - GGGTACGTGG TTGCCGGCCC GGTCTCCGCA GTCCCCACCG AGCCCCGACC CT -              #CCTGGCCG     60                                                                  - - CCCCCTCGCC TTACCTCGTC GCC ATG CGC CTC CGC CGC CT - #A GCG CTG TTC             110                                                                                         - #        Met Arg Leu Arg Arg Leu - #Ala Leu Phe                              - #          1        - #       5                             - - CCA GGC CTG GCG CTG CTC CTC GCC GCG GCC CG - #C CTC GCT GCT GCC TCC           158                                                                        Pro Gly Leu Ala Leu Leu Leu Ala Ala Ala Ar - #g Leu Ala Ala Ala Ser             10                 - # 15                 - # 20                 - # 25        - - GAT GTG CTG GAA CTC ACG GAC GAC AAC TTC GA - #G AGT CGC ATC ACC GAC           206                                                                        Asp Val Leu Glu Leu Thr Asp Asp Asn Phe Gl - #u Ser Arg Ile Thr Asp                             30 - #                 35 - #                 40               - - ACG GGC TCT TCT GGC CTC ATG CTC GTC GAG TT - #C TTC GCC CCC TGG TGT           254                                                                        Thr Gly Ser Ser Gly Leu Met Leu Val Glu Ph - #e Phe Ala Pro Trp Cys                         45     - #             50     - #             55                   - - GGA CAC TGC AAA AAG CTT GCC CCA GAG TAT GA - #A GCT GCA GCT ACC AGA           302                                                                        Gly His Cys Lys Lys Leu Ala Pro Glu Tyr Gl - #u Ala Ala Ala Thr Arg                     60         - #         65         - #         70                       - - TTA AAA GGA ATA GTC CCG TTA GCA AAG GTG GA - #T TGT ACT GCC AAC ACG           350                                                                        Leu Lys Gly Ile Val Pro Leu Ala Lys Val As - #p Cys Thr Ala Asn Thr                 75             - #     80             - #     85                           - - AAC ACC TGT AAT AAG TAT GGA GTG AGT GGA TA - #T CCA ACC CTG AAG ATA           398                                                                        Asn Thr Cys Asn Lys Tyr Gly Val Ser Gly Ty - #r Pro Thr Leu Lys Ile             90                 - # 95                 - #100                 - #105        - - TTT AGA GAT GGT GAA GAA TCA GGT GCC TAT GA - #T GGG CCT AGG ACT GCC           446                                                                        Phe Arg Asp Gly Glu Glu Ser Gly Ala Tyr As - #p Gly Pro Arg Thr Ala                            110  - #               115  - #               120               - - GAT GGA ATT GTC AGC CAC CTG AAG AAA CAG GC - #T GGA CCA GCT TCA GTT           494                                                                        Asp Gly Ile Val Ser His Leu Lys Lys Gln Al - #a Gly Pro Ala Ser Val                        125      - #           130      - #           135                   - - CCT CTC AAG TCT GAG GAA GAA TTT GAA AAG TT - #C ATT AGC GAT AAA GAT           542                                                                        Pro Leu Lys Ser Glu Glu Glu Phe Glu Lys Ph - #e Ile Ser Asp Lys Asp                    140          - #       145          - #       150                       - - GCT TCT GTG GTG GGT TTT TTC AAG GAT TTA TT - #C AGT GAA GCT CAC TCT           590                                                                        Ala Ser Val Val Gly Phe Phe Lys Asp Leu Ph - #e Ser Glu Ala His Ser                155              - #   160              - #   165                           - - GAG TTT CTA AAA GCA GCC AGC AAC TTG AGG GA - #T AAC TAC CGG TTT GCA           638                                                                        Glu Phe Leu Lys Ala Ala Ser Asn Leu Arg As - #p Asn Tyr Arg Phe Ala            170                 1 - #75                 1 - #80                 1 -       #85                                                                               - - CAC ACC AAT GTT GAA TCT CTG GTG AAC AAA TA - #C GAT GAC GAT GGA         GAG      686                                                                     His Thr Asn Val Glu Ser Leu Val Asn Lys Ty - #r Asp Asp Asp Gly Glu                           190  - #               195  - #               200               - - GGT ATC ACC TTG TTT CGT CCT TCC CAT CTG AC - #G AAC AAG TTT GAA GAC           734                                                                        Gly Ile Thr Leu Phe Arg Pro Ser His Leu Th - #r Asn Lys Phe Glu Asp                        205      - #           210      - #           215                   - - AAG ACT GTG GCA TAT ACA GAA CAG AAA ATG AC - #C AGT GGG AAG ATT AAA           782                                                                        Lys Thr Val Ala Tyr Thr Glu Gln Lys Met Th - #r Ser Gly Lys Ile Lys                    220          - #       225          - #       230                       - - AGA TTT ATT CAG GAA AAC ATT TTT GGT ATC TG - #C CCT CAC ATG ACA GAA           830                                                                        Arg Phe Ile Gln Glu Asn Ile Phe Gly Ile Cy - #s Pro His Met Thr Glu                235              - #   240              - #   245                           - - GAC AAT AAA GAT TTA CTA CAG GGC AAG GAT TT - #A CTC ATC GCT TAC TAT           878                                                                        Asp Asn Lys Asp Leu Leu Gln Gly Lys Asp Le - #u Leu Ile Ala Tyr Tyr            250                 2 - #55                 2 - #60                 2 -       #65                                                                               - - GAT GTG GAC TAT GAA AAG AAT GCT AAA GGT TC - #C AAC TAC TGG AGA         AAC      926                                                                     Asp Val Asp Tyr Glu Lys Asn Ala Lys Gly Se - #r Asn Tyr Trp Arg Asn                           270  - #               275  - #               280               - - AGA GTA ATG ATG GTG GCA AAG AAA TTC CTG GA - #T GCT GGG CAG AAA CTC           974                                                                        Arg Val Met Met Val Ala Lys Lys Phe Leu As - #p Ala Gly Gln Lys Leu                        285      - #           290      - #           295                   - - CAT TTT GCT GTA GCT AGC CGT AAA ACC TTT AG - #C CAT GAA CTT TCA GAT          1022                                                                        His Phe Ala Val Ala Ser Arg Lys Thr Phe Se - #r His Glu Leu Ser Asp                    300          - #       305          - #       310                       - - TTT GGC TTG GAA AGC ACT ACT GGA GAG ATT CC - #T GTT GTT GCT GTC AGA          1070                                                                        Phe Gly Leu Glu Ser Thr Thr Gly Glu Ile Pr - #o Val Val Ala Val Arg                315              - #   320              - #   325                           - - ACC GCA AAA GGA GAG AAG TTT GTC ATG CAG GA - #G GAG TTC TCG CGT GAT          1118                                                                        Thr Ala Lys Gly Glu Lys Phe Val Met Gln Gl - #u Glu Phe Ser Arg Asp            330                 3 - #35                 3 - #40                 3 -       #45                                                                               - - GGC AAG GCT CTT GAG AGA TTC CTG GAG GAT TA - #C TTT GAC GGC AAC         CTG     1166                                                                     Gly Lys Ala Leu Glu Arg Phe Leu Glu Asp Ty - #r Phe Asp Gly Asn Leu                           350  - #               355  - #               360               - - AAG AGA TAC CTG AAG TCT GAG CCT ATC CCT GA - #G AGC AAT GAT GGG CCT          1214                                                                        Lys Arg Tyr Leu Lys Ser Glu Pro Ile Pro Gl - #u Ser Asn Asp Gly Pro                        365      - #           370      - #           375                   - - GTA AAG GTA GTG GTA GCA GAG AAT TTT GAT GA - #A ATA GTG AAT AAT GAA          1262                                                                        Val Lys Val Val Val Ala Glu Asn Phe Asp Gl - #u Ile Val Asn Asn Glu                    380          - #       385          - #       390                       - - AAT AAA GAT GTG CTG ATT GAG TTT TAT GCT CC - #T TGG TGT GGT CAC TGT          1310                                                                        Asn Lys Asp Val Leu Ile Glu Phe Tyr Ala Pr - #o Trp Cys Gly His Cys                395              - #   400              - #   405                           - - AAG AAT CTG GAG CCT AAG TAT AAA GAA CTG GG - #A GAG AAG CTC AGA AAA          1358                                                                        Lys Asn Leu Glu Pro Lys Tyr Lys Glu Leu Gl - #y Glu Lys Leu Arg Lys            410                 4 - #15                 4 - #20                 4 -       #25                                                                               - - GAT CCA AAT ATT GTC ATA GCC AAG ATG GAT GC - #T ACA GCC AAC GAT         GTG     1406                                                                     Asp Pro Asn Ile Val Ile Ala Lys Met Asp Al - #a Thr Ala Asn Asp Val                           430  - #               435  - #               440               - - CCT TCT CCA TAT GAA GTC AGA GGT TTT CCT AC - #C ATC TAC TTC TCT CCA          1454                                                                        Pro Ser Pro Tyr Glu Val Arg Gly Phe Pro Th - #r Ile Tyr Phe Ser Pro                        445      - #           450      - #           455                   - - GCC AAC AAG AAG CAA AAT CCA AAG AAA TAT GA - #A GGT GGC CGT GAA TTA          1502                                                                        Ala Asn Lys Lys Gln Asn Pro Lys Lys Tyr Gl - #u Gly Gly Arg Glu Leu                    460          - #       465          - #       470                       - - AGT GAT TTT ATT AGC TAT CTA AAG CGA GAG GC - #T ACA AAC CCC CCT GTA          1550                                                                        Ser Asp Phe Ile Ser Tyr Leu Lys Arg Glu Al - #a Thr Asn Pro Pro Val                475              - #   480              - #   485                           - - ATT CAA GAA GAA AAA CCC AAG AAG AAG AAG AA - #G GCA CAG GAG GAT CTC          1598                                                                        Ile Gln Glu Glu Lys Pro Lys Lys Lys Lys Ly - #s Ala Gln Glu Asp Leu            490                 4 - #95                 5 - #00                 5 -       #05                                                                               - - TAA AGCAGCAGCC AAACATCATA TACTTTGTCA AAGGACTTTT CCACCAGAG - #A               1651                                                                        *                                                                              - - TGGGAAAACC AATGGGGAGG ACTGGGACCC GTATGGGAAT TACTGCCTCT CA -              #GGGCTGAG   1711                                                                  - - AGGGCAGAAT GGTTATAATC TGAGTCCTGT TAAATTTTCT CTAAACTGTT TC -             #TTAGCTGC   1771                                                                  - - ACTGTTTATG AAAATACCAG AACCAGTTTA TGTTTGTGGT TTTGGGAAAA TT -             #ATTTGTGT   1831                                                                  - - TGAGGGGAAT GTTGTGGGGG TGGGGGGAAT TGAGTTGGGG GGTTATTTTC TA -             #ATTTTTTT   1891                                                                  - - TGTACATTTG GAACAGTGAC AATAAATGCG CCCCCTTTAA AAAAAAAAAA A - #                1942                                                                         - -  - - (2) INFORMATION FOR SEQ ID NO:4:                                      - -      (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH:  506 ami - #no acids                                               (B) TYPE: amino acid                                                           (D) TOPOLOGY: linear                                                  - -     (ii) MOLECULE TYPE: protein                                            - -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:4:                                - - Met Arg Leu Arg Arg Leu Ala Leu Phe Pro Gl - #y Leu Ala Leu Leu Leu         1               5 - #                 10 - #                 15               - - Ala Ala Ala Arg Leu Ala Ala Ala Ser Asp Va - #l Leu Glu Leu Thr Asp                    20     - #             25     - #             30                   - - Asp Asn Phe Glu Ser Arg Ile Thr Asp Thr Gl - #y Ser Ser Gly Leu Met                35         - #         40         - #         45                       - - Leu Val Glu Phe Phe Ala Pro Trp Cys Gly Hi - #s Cys Lys Lys Leu Ala            50             - #     55             - #     60                           - - Pro Glu Tyr Glu Ala Ala Ala Thr Arg Leu Ly - #s Gly Ile Val Pro Leu        65                 - # 70                 - # 75                 - # 80        - - Ala Lys Val Asp Cys Thr Ala Asn Thr Asn Th - #r Cys Asn Lys Tyr Gly                        85 - #                 90 - #                 95               - - Val Ser Gly Tyr Pro Thr Leu Lys Ile Phe Ar - #g Asp Gly Glu Glu Ser                   100      - #           105      - #           110                   - - Gly Ala Tyr Asp Gly Pro Arg Thr Ala Asp Gl - #y Ile Val Ser His Leu               115          - #       120          - #       125                       - - Lys Lys Gln Ala Gly Pro Ala Ser Val Pro Le - #u Lys Ser Glu Glu Glu           130              - #   135              - #   140                           - - Phe Glu Lys Phe Ile Ser Asp Lys Asp Ala Se - #r Val Val Gly Phe Phe       145                 1 - #50                 1 - #55                 1 -       #60                                                                               - - Lys Asp Leu Phe Ser Glu Ala His Ser Glu Ph - #e Leu Lys Ala Ala         Ser                                                                                              165  - #               170  - #               175              - - Asn Leu Arg Asp Asn Tyr Arg Phe Ala His Th - #r Asn Val Glu Ser Leu                   180      - #           185      - #           190                   - - Val Asn Lys Tyr Asp Asp Asp Gly Glu Gly Il - #e Thr Leu Phe Arg Pro               195          - #       200          - #       205                       - - Ser His Leu Thr Asn Lys Phe Glu Asp Lys Th - #r Val Ala Tyr Thr Glu           210              - #   215              - #   220                           - - Gln Lys Met Thr Ser Gly Lys Ile Lys Arg Ph - #e Ile Gln Glu Asn Ile       225                 2 - #30                 2 - #35                 2 -       #40                                                                               - - Phe Gly Ile Cys Pro His Met Thr Glu Asp As - #n Lys Asp Leu Leu         Gln                                                                                              245  - #               250  - #               255              - - Gly Lys Asp Leu Leu Ile Ala Tyr Tyr Asp Va - #l Asp Tyr Glu Lys Asn                   260      - #           265      - #           270                   - - Ala Lys Gly Ser Asn Tyr Trp Arg Asn Arg Va - #l Met Met Val Ala Lys               275          - #       280          - #       285                       - - Lys Phe Leu Asp Ala Gly Gln Lys Leu His Ph - #e Ala Val Ala Ser Arg           290              - #   295              - #   300                           - - Lys Thr Phe Ser His Glu Leu Ser Asp Phe Gl - #y Leu Glu Ser Thr Thr       305                 3 - #10                 3 - #15                 3 -       #20                                                                               - - Gly Glu Ile Pro Val Val Ala Val Arg Thr Al - #a Lys Gly Glu Lys         Phe                                                                                              325  - #               330  - #               335              - - Val Met Gln Glu Glu Phe Ser Arg Asp Gly Ly - #s Ala Leu Glu Arg Phe                   340      - #           345      - #           350                   - - Leu Glu Asp Tyr Phe Asp Gly Asn Leu Lys Ar - #g Tyr Leu Lys Ser Glu               355          - #       360          - #       365                       - - Pro Ile Pro Glu Ser Asn Asp Gly Pro Val Ly - #s Val Val Val Ala Glu           370              - #   375              - #   380                           - - Asn Phe Asp Glu Ile Val Asn Asn Glu Asn Ly - #s Asp Val Leu Ile Glu       385                 3 - #90                 3 - #95                 4 -       #00                                                                               - - Phe Tyr Ala Pro Trp Cys Gly His Cys Lys As - #n Leu Glu Pro Lys         Tyr                                                                                              405  - #               410  - #               415              - - Lys Glu Leu Gly Glu Lys Leu Arg Lys Asp Pr - #o Asn Ile Val Ile Ala                   420      - #           425      - #           430                   - - Lys Met Asp Ala Thr Ala Asn Asp Val Pro Se - #r Pro Tyr Glu Val Arg               435          - #       440          - #       445                       - - Gly Phe Pro Thr Ile Tyr Phe Ser Pro Ala As - #n Lys Lys Gln Asn Pro           450              - #   455              - #   460                           - - Lys Lys Tyr Glu Gly Gly Arg Glu Leu Ser As - #p Phe Ile Ser Tyr Leu       465                 4 - #70                 4 - #75                 4 -       #80                                                                               - - Lys Arg Glu Ala Thr Asn Pro Pro Val Ile Gl - #n Glu Glu Lys Pro         Lys                                                                                              485  - #               490  - #               495              - - Lys Lys Lys Lys Ala Gln Glu Asp Leu  *                                                500      - #           505                                          - -  - - (2) INFORMATION FOR SEQ ID NO:5:                                      - -      (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 6 amino - #acids                                                   (B) TYPE: amino acid                                                           (C) STRANDEDNESS:                                                              (D) TOPOLOGY: Not Relev - #ant                                        - -     (ii) MOLECULE TYPE: peptide                                            - -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:5:                                - - Trp Cys Gly His Cys Lys                                                   1               5                                                               - -  - - (2) INFORMATION FOR SEQ ID NO:6:                                      - -      (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 6 amino - #acids                                                   (B) TYPE: amino acid                                                           (C) STRANDEDNESS:                                                              (D) TOPOLOGY: Not Relev - #ant                                        - -     (ii) MOLECULE TYPE: peptide                                            - -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:6:                                - - Trp Cys Gly Pro Cys Lys                                                   1               5                                                               - -  - - (2) INFORMATION FOR SEQ ID NO:7:                                      - -      (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 30 base - #pairs                                                   (B) TYPE: nucleic acid                                                         (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: linear                                                  - -     (ii) MOLECULE TYPE: other nucleic acid                                          (A) DESCRIPTION: /desc - #= "mutagenic primer"                        - -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:7:                                - - GCCCCCTGGT CTCCACACAG CAAAAAGCTT         - #                  - #                30                                                                       - -  - - (2) INFORMATION FOR SEQ ID NO:8:                                      - -      (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 30 base - #pairs                                                   (B) TYPE: nucleic acid                                                         (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: linear                                                  - -     (ii) MOLECULE TYPE: other nucleic acid                                          (A) DESCRIPTION: /desc - #= "mutagenic primer"                        - -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:8:                                - - GCTCCTTGGT CTGGTCACTC TAAGAATCTG         - #                  - #                30                                                                     __________________________________________________________________________ 

We claim:
 1. An isolated human phospholipase C-α polypeptide comprising an amino acid sequence from Ser at position 25 to Leu at the position 505 of SEQ ID NO:
 2. 2. A polypeptide according to claim 1, comprising an amino acid sequence from Met at the position 1 to Leu at position 505 of SEQ ID NO:
 2. 3. A DNA sequence encoding the polypeptide of claim 1 or
 2. 4. An expression vector comprising the DNA sequence of claim
 3. 5. A transformed host cell obtained by introducing the expression vector of claim
 4. 